The best replacement for memcached is redis.

The best alternatives to memcached are rated as following:
★★★★★  redis
★★★★★  ehcache
★★★  apc
★★★  varnish
★★  memcache
★★  membase
★★  couchbase
★★  coherence
★★  appfabric
★  redis benchmark
★  nosql
★  dynamodb
★  eaccelerator
  .net cache
  cassandra
  libmemcached
  xcache
  jcs

Your alternative for memcached is not listed? Suggest!
Speaking about memcached, one probably shouldn't forget about hibernate.

Other search terms related to memcached and their ratings are:
★★★★★ hibernate
★ libevent
★ magento
You have in mind a companion for memcached and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of memcached in all years. Click on graph for more.
memcached
redis
ehcache